Traditional Hammer Curls
Hammer curls are essential for the development of the brachioradialis, a muscle in the forearm. Using a neutral grip hand position – palms facing each other – gives you a mechanical advantage so that you can produce force over the biceps and elbow flexor group.
That's fine for aesthetics, but it's limited. The prime mover of this exercise doesn't cross the wrist joint, so there's not much transference into grip strength.
When it comes to functional hypertrophy of the arms, the slight angles for both hand and shoulder positions are far more advantageous than the common fully pronated, fully supinated, and neutral grip positions with a neutral shoulder. Why? Because the body functions in spiraling groups of muscle, fascia, and neural connections. These create tension. So limiting this irradiation reflex doesn't make sense. Instead, train it directly.
The Hybrid Hammer Curl
The hybrid hammer reverse curl places the hands in a slightly pronated position, which still hits the brachioradialis and biceps, but also the wrist extensor group. The wrist extensors stabilize the wrist and elbow joints in order for the bigger flexor group to fire hard and recruit more fibers into isometric actions.
Doing this exercise with the wrist in slight extension and gripping the dumbbells as hard as you possibly can will create force up the kinetic chain of the arms, increasing activation in the big movers while challenging the small intrinsic muscles.
Chase the pump for this. Think high reps, slow movements, and hard squeezes at the top. Make these hurt. Your forearms will grow and your grip strength will go through the roof.